In the past few years there has been an increased interest in a new type of laser device called a vertical cavity surface emitting laser (VCSEL). Advantages of VCSEL devices are that the device is smaller, has potentially higher performance, and is potentially more manufacturable. These advantages are due in part from advances in epitaxial deposition techniques such as metal organic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE).
However, even with these advances in deposition techniques there is difficulty during manufacturing in controlling the mode of operation of the laser while maintaining high output power. VCSELs are formed by depositing a plurality of layers on a substrate to form the VCSEL. See, for example, U.S. Pat. No. 5,034,092, entitled "PLASMA ETCHING OF SEMICONDUCTOR SUBSTRATES", issued Jul. 23, 1991, assigned to the same assignee and included herein by this reference, and U.S. Pat. No. 5,256,596, entitled "TOP EMITTING VCSEL WITH IMPLANT", issued Oct. 26, 1993, assigned to the same assignee and included herein by this reference.
VCSELs generally include a first distributed Bragg reflector (DBR), also referred to as a mirror stack, formed on top of a substrate by semiconductor manufacturing techniques, an active region formed on top of the first mirror stack, and a second mirror stack formed on top of the active region. The VCSEL is driven by current forced through the active region, typically achieved by providing a first contact on the reverse side of the substrate and a second contact on top of the second mirror stack.
The use of mirror stacks in VCSELs is well established in the art. Typically, mirror stacks are formed of multiple pairs of layers often referred to as mirror pairs. The pairs of layers are formed of a material system generally consisting of two materials having different indices of refraction and being easily lattice matched to the other portions of the VCSEL. For example, a GaAs based VCSEL typically uses an AlAs/GaAs or AlGaAs/AlAs material system wherein the different refractive index of each layer of a pair is achieved by altering the aluminum content in the layers. In conventional devices, the number of mirror pairs per stack may range from 20 to 40 to achieve a high percentages of reflectivity, depending on the difference between the refractive indices of the layers. The large number of pairs increases the percentage of reflected light.
In conventional VCSELs, conventional material systems perform adequately. However, new products are being developed requiring VCSELs to operate in a stable high order mode of operation. These types of VCSELs are of great interest in the optical telecommunication and optical data storage industries. Typically it is difficult to achieve a stable single high order mode output from a multi mode VCSEL. Traditionally, single mode output VCSELs have been achieved by shrinking the VCSEL device size to force laser operation in the fundamental/lowest order mode of operation. As a result, the small device size operates to have a low output power.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object of the present invention to provide a new and improved stable high power single high order mode VCSEL fabricated as a annular waveguide VCSEL.
Another object of the invention is to provide a reliable high power single high order mode VCSEL.
Yet another object of the invention is to reduce the complexity of fabricating a high power single high order mode VCSEL.
Another object of the present invention is to provide for a method of fabricating an annular waveguide VCSEL that includes the etching of a second mirror stack so as to force the lasing mode to be confined to an annular region thereby forcing the VCSEL to operate in a single high order mode.